Scientists now wait for the 'dragons' of Mars to appear

An artist's impression shows the rover as it was expected to go about its work.
Picture: AFP

"Here Be Dragons." As ancient mapmakers groped for words to describe the terra incognita beyond the edge of the world, they settled on these none-too-encouraging words. It was all mariners of the time had to go on.

The modern mariners at the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena are now ready to meet their own dragons as their robot, Spirit, landed on the alien world of Mars yesterday.

If Spirit survives, it will be the most ambitious explorer ever to roam an alien world, its mission no less than a search for signs of water that would have once allowed life to bloom on Mars.

But like their ancient counterparts, the scientists at the laboratory are most worried about the devils they don't - and can't - know.

"You just hope your imagination is wide enough to think of all the possibilities," said Rob Manning, who heads the Mars rover landing team.

"It's not inconceivable that Mars could throw something at us significantly outside our expectations."

Mars, after all, is no place like home. The sky is pink, the sunset blue. The temperature can be 30 degrees colder at your head than at your feet - meaning you could walk around barefoot yet have to wear a wool hat.

There's practically no atmosphere, and most of the landing site - a 4 billion-year-old crater - "has no analogue with anything on Earth", geologist Matthew Golombek said.

Already two NASA orbiters have been madly snapping bird's-eye pictures, taking the planet's temperature, mapping its topology and reading its chemistry.

Their efforts have made Gusev Crater the most studied place on Mars.

Even so, the satellites cannot make out features smaller than about five metres, meaning that very large green monsters indeed could be waiting below - or, scarier still, very sharp rocks.

A long string of much-talked-about Mars failures added to the pressure to set Spirit down safely; but so, too, has success.

Eight years ago, Pathfinder bounced onto Mars for a picture-perfect landing; its toy-like rover, Sojourner, wobbled around the surface for months, winning the hearts of the world - and bringing more people to the NASA website than any event in internet history.

You almost wished it hadn't been quite so perfect, project system engineer Jennifer Trosper said. "People would have lower expectations. Pathfinder didn't have such a 'this has to work' mentality."

Spirit and its twin, Opportunity (due to land this month), are far more ambitious, expensive and heavier - 175 kilograms each, more than 15 times Sojourner's weight.

"It's a chance to redeem ourselves," Ms Trosper said.

"We want to prove to the world that we can do complicated stuff and do it right."

The system has been tested many times over, so engineers at the laboratory say they are confident it will work.

But ultimately, each pyrotechnic bolt, each airbag, each rocket, is a single-use affair, a one-shot event.